Question about Koenig HeatsBox Go

I wanted to find out more about the Heatbox Go. I've had the box for about 2 months now and am actually very happy with it. I just saw that the description says that you can heat several meals with the box. However, I have the problem that after heating up one meal my battery is already below 10 %. Is it just me who has the problem with the battery, or is it just not that good in general? What I actually find a 'no go' for the price